In order to reduce heat losses, insulation is used on most pipes carrying high temperature fluids. Presently, one common type of insulation used in high temperature situations is a molded jacket, formed in cylindrical halves, consisting of a fibrous material such as mineral fibers. Although this forms an adequate thermal barrier, it is very expensive to make. The fibers are generally wound around a cylindrical mandrel, cured so that they are thermally set, and then cut into semicylindrical pieces which can be later reassembled on the pipe to be insulated.
If these semicylindrical members could be cut from mineral fibers in board or block form, they would be much cheaper to make. However, until the present invention, this has not been possible. Pipe insulation cut from block or board insulation results in physical differences from the molded product. The molded insulation, where the fibers are wound around the mandrel, has fibers whose axes are always perpendicular to the direction of heat flow from the pipe. This is the optimum orientation with regard to the prevention of heat transfer. The insulation cut from board insulation has fibers ranging from perpendicular to parallel with the heat flow from the pipe. This form of insulation is considerably cheaper to fabricate, but is less efficient in preventing heat transfer. Heat transfer in insulation takes three main forms; air conduction, fiber conduction, and radiation. Tests show that mineral fiberboard suffers a substantial nonlinear increase in heat loss in the high temperature range. This indicates radiation as the predominate cause of heat loss. Radiation heat transfer is most easily controlled by increasing material density. If a way were found to selectively increase the material density where required, radiant losses could be minimized and the fiberboard insulation would approach the thermal efficiency of the more expensive molded type.